Its hard to imagine how software installed on your machine could disable the button though I suppose anything is possible. I could see how it could block the popup if you have any browser toolbars installed.
What I would try first is open your browser and go to google, don't have any tabs open with your sites yet.
Clear the browser cache of all cached content.
Now visit your site and see if the problem persists.
If it persists try a different browser to see if it happens in all browsers. If you normally use IE try Firefox, or vice versa.
Hope it helps,